Performance and Mechanical Standards
The gas turbine is a complex machine， and its performance and reliability are governed by many standards. The American Society of Mechanical Engineers (ASME) performance test codes have been written to ensure thattest， are conducted in a manner that guarantees that all turbines are tested under the same set of rules and conditions to ensure that the test results can becomparedinajudiciousmanner. Thereliabilityoftheturbinesdependon the mechanical codes that govern the design of many gas turbines. The mechanical standards and codes have been written by both ASME and the American Petroleum Institute (API).
Major Variables for a Gas Turbine Application
The major variables that affect the gas turbines are the following factors:
1.
Type of application
2.
Plant location and site configuration
3.
Plant size and efficiency
4.
Type of fuel
5.
Enclosures
6.
Plant operation mode; base or peaking
7.
Start-up techniques
Each of the above points are discussed in the following sections.
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Type of Application
The gas turbine is used in many applications， and the application determines in most parts the type of gas turbine best suited. The three major types ofapplications are aircraft propulsion， power generation， and mechanical drives.
Aircraft Propulsion. The aircraft propulsion gas turbines can be sub-divided into two majorcategories， the jet propulsion and turboprop engines. The jet engine consists of a gasifier section and a propulsive thrust section as shown in Figure 4-1. The gasifier section is the section of theturbine， which produces high pressure and temperature gas for the power turbine. This comprises of a compressor section and a turbine section. the sole job of the gasifier turbine section is to drive the gas turbine compressor. This section has one or two shafts. The two-shaft gasifier section usually exists in the new high pressure type gas turbine where the compressorproduces a very high pressure ratio， and has two different sections. Each section is comprised many stages. The two different compressor sectionsconsist of the low pressure compressor section， followed by a high-pressuresection. Each section may have between 10 to15， stages. The jet enginehas a nozzle following the gasifier turbine， which produces the thrust for the engine. In the newer jet turbines the compressor also has a fan section ahead of the turbine and a large amount of the air from the fan section by-passes the rest of the compressor and produces thrust. The thrust from the fan amounts to more than the thrust from the exhaust.
The jet engine has lead the field of gas turbines in firing temperatures. Pressure ratio of 40:1 with firing temperatures reaching 2500 oF (1371 oc)， is now the mode of operation of these engines.
The turboprop engine has a power turbine instead of the nozzle as seen in Figure 4-2. The power turbine drives the propeller. The unit shownschematically is a two-shaft unit， this enables the speed of the propeller tobe better controlled， as the gasifier turbine can then operate at a nearly constant speed. Similar engines are used in helicopter drive applications and many have axial flow compressors with a last stage as a centrifugal compressor as shown in Figure 1-14.
Mechanical Drives. Mechanical drive gas turbines are widely used to drive pumps and compressors. Their application is widely used by offshore and petrochemical industrial complexes. These turbines must be operated at various speeds and thus usually have a gasifier section and a power section.These units in most cases are aero-derivative turbines， turbines， which were originally designed for aircraft application. There are some smaller frametype units， which have been converted to mechanical drive units with a gasifier and power turbine.
Power Generation. The power generation turbines can be further divided into three categories:
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